Ejecta from Van de Graaff Crater

Van de Graaff crater is located on the farside of the Moon south of Aitken crater, at about latitude -27.9, longitude 172.8. Two merged craters make up the formation known as Van de Graaff crater, named after the American physicist. Unlike other merged craters on the Moon, there is no rim separating the two "sections" of the crater. A relatively strong magnetic field was detected near this crater by the Apollo 15 subsatellite magnetometer. This discovery was unusual for the lunar surface because the Moon does not currently have a global magnetic field like the Earth does. Also, Van de Graaff and the surrounding area also have slightly higher concentrations of thorium, a radioactive metal. Are the two observations related?
Section of WAC global mosaic showing Van de Graaff crater. Look at the crater walls to see the unique grooved texture. Resolution is 400 m/pixel [NASA/GSFC/Arizona State University